framework tools/tmux: exact session matching in discovery AND sender target (codex PR #1466)

tmux target syntax accepts an unambiguous PREFIX, so both the socket
discovery loop and the sender's -t could match X-old for target X.
Discovery now probes has-session -t =NAME; the sender target gets '='
prepended unless it is already exact or compound (session:win.pane).
Arm A3 proves it: a prefix-named session no longer swallows a delivery
aimed at the shorter name (sender fails target-not-found rc 1).

packages/mosaic/framework/tools/tmux/agent-send.sh

@@ -178,7 +178,10 @@ if [ -z "$SOCKET_NAME" ] && [ -z "$SSH_TARGET" ]; then
   for sf in "$socket_dir"/*; do
     [ -S "$sf" ] || continue
     sname="${sf##*/}"
-    tmux -L "$sname" has-session -t "$DST_SESSION" 2>/dev/null && hits="$hits$sname"$'\n'
+    # '=' forces exact session-name matching: tmux target syntax otherwise
+    # accepts an unambiguous PREFIX, so a session named X-old on a socket
+    # would count as a false hit for target X (codex PR #1466).
+    tmux -L "$sname" has-session -t "=$DST_SESSION" 2>/dev/null && hits="$hits$sname"$'\n'
   done
   hit_count=$(printf '%s' "$hits" | grep -c . || true)
   if [ "$hit_count" -gt 1 ]; then
@@ -196,11 +199,21 @@ if [ -n "$SOCKET_NAME" ]; then
   socket_args=(-L "$SOCKET_NAME")
 fi
 
+# Exact session matching for the sender target too (codex PR #1466): without
+# '=', tmux target syntax accepts an unambiguous PREFIX, so a delivery aimed
+# at session X can land in X-old. Compound targets (session:win.pane) and
+# already-exact ('=...') forms pass through untouched.
+DST_TARGET="$DST_SESSION"
+case "$DST_SESSION" in
+  =*|*:*) ;;
+  *) DST_TARGET="=$DST_SESSION" ;;
+esac
+
 if [ -z "$SSH_TARGET" ]; then
   # Local pane: call the canonical sender directly.
-  exec "$SENDER" "${socket_args[@]}" -t "$DST_SESSION" -b "$B64" -r "$RETRIES" $vflag
+  exec "$SENDER" "${socket_args[@]}" -t "$DST_TARGET" -b "$B64" -r "$RETRIES" $vflag
 else
   # Remote pane: ship the sender over ssh and run it local to the target.
   ssh -o ConnectTimeout=10 "$SSH_TARGET" \
-      "bash -s -- ${socket_args[*]@Q} -t '$DST_SESSION' -b '$B64' -r '$RETRIES' $vflag" < "$SENDER"
+      "bash -s -- ${socket_args[*]@Q} -t '$DST_TARGET' -b '$B64' -r '$RETRIES' $vflag" < "$SENDER"
 fi

packages/mosaic/framework/tools/tmux/test-send-message-socket.sh

@@ -121,6 +121,24 @@ tmux -L "$SOCKET" kill-session -t "$TWIN" >/dev/null 2>&1 || true
 
 # Arm B: session unique to ONE socket, no -L -> auto-resolve to that socket
 # and deliver there.
+# Arm A3: prefix matching must not produce false socket hits (codex PR
+# #1466): a session named TWIN-old must not count as a hit for target
+# TWIN (tmux target syntax prefix-matches without '=').
+PSEUDO="${TWIN}-old"
+tmux new-session -d -s "$PSEUDO" -c "$TMPDIR" 'PS1="❯ " exec bash --noprofile --norc -i'
+A3_ERR=$(mktemp)
+a3_rc=0
+env -u MOSAIC_TMUX_SOCKET "$AGENT_SEND" -s "$TWIN" -m "prefix trap" >/dev/null 2>"$A3_ERR" || a3_rc=$?
+# TWIN exists nowhere (both twins killed after arm A2); with '=' the
+# PSEUDO session is not a hit, so the sender must fail target-not-found
+# (rc 1) instead of delivering into the prefix-named session.
+[ "$a3_rc" -eq 1 ] || fail "prefix false-hit: rc=$a3_rc want 1 (stderr: $(cat "$A3_ERR"))"
+if tmux capture-pane -t "=$PSEUDO:0.0" -p 2>/dev/null | grep -qF "prefix trap"; then
+  fail "delivery landed in the prefix-named session (false socket hit)"
+fi
+tmux kill-session -t "$PSEUDO" >/dev/null 2>&1 || true
+rm -f "$A3_ERR"
+
 uniq_rc=0
 env -u MOSAIC_TMUX_SOCKET "$AGENT_SEND" -s "$TARGET" -m "autoresolved hello" >$UNIQ_OUT 2>$UNIQ_ERR || uniq_rc=$?
 [ "$uniq_rc" -eq 0 ] || fail "unique auto-resolution: rc=$uniq_rc (stderr: $(cat $UNIQ_ERR))"